1. Field of the Invention
Embodiments of the invention generally relate to a method and apparatus for distributing fluid in a chemical mechanical polishing system.
2. Description of the Related Art
In semiconductor wafer processing, the use of chemical mechanical planarization, or CMP, has gained favor due to the enhanced ability to increase device density on a semiconductor workpiece, or substrate, such as a wafer. Chemical mechanical planarization systems generally utilize a polishing head to retain and press a substrate against a polishing surface of a polishing material while providing motion therebetween. Some planarization systems utilize a polishing head that is moveable over a stationary platen that supports the polishing material. Other systems utilize different configurations to provide relative motion between the polishing material and the substrate, for example, providing a rotating platen. A polishing fluid is typically disposed between the substrate and the polishing material during polishing to provide chemical activity that assists in the removal of material from the substrate. Some polishing fluids may also contain abrasives.
One of the challenges in developing robust polishing systems and processes is controlling the uniformity of material removed across the polished surface of the substrate. For example, as the substrate travels across the polishing surface, the edge of the substrate is often polished at a higher rate. This is due in part to the tendency of the substrate to “nose drive” due to frictional forces as the substrate moves across the polishing surface.
Another problem affecting polishing uniformity across the substrate's surface is the tendency of some materials to be removed faster than the surrounding materials. For example, copper is generally removed more rapidly than the material surrounding the copper material (typically an oxide) during polishing. The faster removal of copper, often referred to a dishing, is particularly evident when the width of the copper surface exceeds five microns.
Although many solutions have been utilized in order to mitigate the non-uniformity of the substrate as a result of polishing, none have proved to be completely satisfactory. Thus, the demand for uniform, highly planarized surfaces is still a paramount concern due to the trend toward smaller decreased line sizes and increased device density.
Therefore, there is a need for improved polishing uniformity in chemical mechanical planarization systems.